fix(#633): 修复一键生成转场时长不生效 - _VirtualClip缺transition_duration字段

根因：_VirtualClip 数据类缺少 transition_duration 字段，导致模板配置的自定义转场时长
在一键生成路径中被静默丢弃，永远使用引擎默认值 0.5s。

修复内容：
1. _VirtualClip 添加 transition_duration 字段（默认0.0，表示用全局默认值）
2. _apply_template_clip_effects 增加 transition_duration 从模板 config 映射
3. UnifiedRenderService 多段裁剪分支 ResolvedClip 构建补上 transition_duration
   （顺便补上同分支遗漏的 playback_speed）
4. 补充 3 个单测用例：正常映射/cut转场忽略/无效值安全跳过

apps/worker/video_processing/unified_render_service.py

@@ -1304,6 +1304,8 @@ class UnifiedRenderService:
                         start_time=seg_start,
                         duration=seg_duration,
                         transition_effect=clip.transition_effect or "cut",
+                        transition_duration=getattr(clip, "transition_duration", 0.0) or 0.0,
+                        playback_speed=getattr(clip, "playback_speed", 1.0) or 1.0,
                         config={**clip_config, "_segment_id": seg.segment_id},
                         actual_duration=actual_duration,
                         trim_config=seg.trim,

apps/worker/worker_app/tasks/generation.py

@@ -171,6 +171,7 @@ class _VirtualClip:
     start_time: float = 0.0
     duration: float = 0.0
     transition_effect: str = "cut"
+    transition_duration: float = 0.0  # 0 表示使用全局默认值
     playback_speed: float = 1.0
     status: str = "ready"
     config: dict[str, Any] = field(default_factory=dict)
@@ -279,7 +280,7 @@ def _apply_template_clip_effects(
         cfg_idx = min(i, len(main_configs) - 1)
         template_cfg = main_configs[cfg_idx]
 
-        # 1. 转场效果
+        # 1. 转场效果 + 时长
         transition = (
             template_cfg.transition_effect.value
             if hasattr(template_cfg.transition_effect, "value")
@@ -287,6 +288,16 @@ def _apply_template_clip_effects(
         )
         if transition and transition != "cut":
             clip.transition_effect = transition
+            # 同步转场时长（模板 clip_config 里的 transition_duration）
+            tpl_cfg = template_cfg.config or {}
+            tpl_duration = tpl_cfg.get("transition_duration")
+            if tpl_duration:
+                try:
+                    dur_val = float(tpl_duration)
+                    if dur_val > 0:
+                        clip.transition_duration = dur_val
+                except (ValueError, TypeError):
+                    pass
 
         # 2. clip 级效果配置（滤镜、调速等）
         template_clip_config = template_cfg.config or {}

tests/unit/test_oneclick_gen_p0_fixes.py

@@ -309,6 +309,8 @@ class TestTemplateClipEffectMapping:
             asset_id: str = f"asset_{idx}"
             duration: float = 5.0
             transition_effect: str = "cut"
+            transition_duration: float = 0.0
+            playback_speed: float = 1.0
             config: dict = field(default_factory=dict)
 
         return FakeClip(config=config or {})
@@ -396,6 +398,54 @@ class TestTemplateClipEffectMapping:
         # 模板是 cut 时，保留原有值（避免无意义覆盖）
         assert clips[0].transition_effect == "fade"
 
+    def test_transition_duration_mapped(self):
+        """转场时长（transition_duration）从模板 config 正确映射到 clip."""
+        from worker_app.tasks.generation import _apply_template_clip_effects
+
+        clips = [self._make_virtual_clip(i) for i in range(3)]
+        clip_configs = [
+            self._make_template_clip_config("main", transition="fade", config={"transition_duration": 0.8}),
+            self._make_template_clip_config("main", transition="dissolve", config={"transition_duration": 1.2}),
+        ]
+
+        _apply_template_clip_effects(clips, clip_configs, "one_take")
+
+        # 前两个按顺序映射，第三个复用最后一个
+        assert clips[0].transition_effect == "fade"
+        assert clips[0].transition_duration == 0.8
+        assert clips[1].transition_effect == "dissolve"
+        assert clips[1].transition_duration == 1.2
+        assert clips[2].transition_effect == "dissolve"
+        assert clips[2].transition_duration == 1.2
+
+    def test_transition_duration_ignored_for_cut(self):
+        """模板转场为 cut 时，transition_duration 不生效（保持默认0）."""
+        from worker_app.tasks.generation import _apply_template_clip_effects
+
+        clips = [self._make_virtual_clip(0)]
+        clip_configs = [
+            self._make_template_clip_config("main", transition="cut", config={"transition_duration": 0.5}),
+        ]
+
+        _apply_template_clip_effects(clips, clip_configs, "one_take")
+
+        # cut 转场不映射，transition_duration 也不应用
+        assert clips[0].transition_duration == 0.0
+
+    def test_transition_duration_invalid_value_skipped(self):
+        """transition_duration 为无效值时安全跳过."""
+        from worker_app.tasks.generation import _apply_template_clip_effects
+
+        clips = [self._make_virtual_clip(0)]
+        clip_configs = [
+            self._make_template_clip_config("main", transition="fade", config={"transition_duration": "abc"}),
+        ]
+
+        _apply_template_clip_effects(clips, clip_configs, "one_take")
+
+        assert clips[0].transition_effect == "fade"
+        assert clips[0].transition_duration == 0.0  # 无效值保持默认
+
     def test_intro_outro_extracted(self):
         """intro/outro 类型 clip_config 正确提取为 plan 级 intro_outro 配置."""
         from worker_app.tasks.generation import _extract_intro_outro_from_clip_configs